Exploring the effect of the ligand design on the interactions between [Ru(η5-C5H5)(PPh3)(N,O)][CF3SO3] complexes and human serum albumin

•Strong interaction of ruthenium compounds with human serum albumin•Ruthenium compounds bind to site I of albumin by hydrophobic forces.•Marginal differences on the ligand structures influence the affinity to albumin.

Ruthenium complexes hold a great potential in chemotherapy as an alternative to the classical platinum based drugs. The organometallic compounds studied in the present work were previously found to exhibit important anticancer activities. Here we have investigated the binding of three ruthenium compounds, namely [Ru(η5-C5H5)(PPh3)(bopy)][CF3SO3] 1, [Ru(η5-C5H5)(PPh3)(2-ap)][CF3SO3] 2, and [Ru(η5-C5H5)(PPh3)(isoquinpk)][CF3SO3] 3 (bopy = 2-benzoylpyridine; 2-ap = 2-acetylpyridine; isoquinpk = 1-isoquinolinyl phenyl ketone) to fatty acid human serum albumin (HSA) and fatty acid-free human serum albumin (HSAfaf) at physiological pH 7.4. The influence of the substituent groups on the heteroaromatic (N,O) coordinated ligand was also studied by fluorescence spectroscopy to get information about this binding. The Stern–Volmer quenching constants (KSV) were calculated at 293, 298 and 310 K, with the corresponding thermodynamic parameters ∆G, ∆H and ∆S as well. The fluorescence quenching method was used to determine the number of binding sites (n) and association constants (Ka) at the same temperatures. The binding site to HSA was confirmed by competitive studies of the ruthenium compounds with warfarin.

Graphical abstractBinding of three Ru(II) organometallic compounds to site I of albumin was studied by fluorescence spectroscopy.Figure optionsDownload full-size imageDownload as PowerPoint slide